The reaction mechanism of the Na-K pump of the red blood cell will be investigated. The effect of ions at the inner and outer surface of the pump and of metabolites at the inner surface of the pump on the pump rate will be investigated and from the results of such studies conclusions about the pump rate will be drawn. The studies will focus upon the effect of internal K as a stimulator of the pump rate. Experiments will be performed to determine whether the effect is the result of an alteration by internal K of the affinity of the pump for external K, internal Na, or Mg, or whether it is upon the maximal pump rate. If the latter proves to be the case, then we still attempt to decide whether internal K exerts its effect by increasing the concentration of ATP within the cell as a result of an effect on one of the glycolytic enzymes, or by altering the affinity of the pump for ATP, ADP or inorganic phosphate. We shall also investigate the effect of oligomycin on the partial reactions of the Na-K pump in an attempt to obtain further evidence that the phosphorylated intermediates of the ATPase reaction are intermediates of the transport reaction. BIBLIOGRAPHIC REFERENCES: Sachs, J.R. (1977). Kinetics of the inhibition of the Na-K pump by external sodium. J. Physiol. (Lond.) 264, 449-470. Kropp, D.L. & Sachs, J.R. (1977). Kinetics of the inhibition of the Na-K pump by tetrapropylammonium chloride. J. Physiol. (Lond.) 264, 471-487.